Human DNA polymerase θ does not harbor intrinsic nuclease activity

DNA polymerase θ (Pol θ) is the enzyme at the heart of theta-mediated end joining (TMEJ), a double-strand break repair pathway.1 The process of aligning microhomologies often results in unpaired 3′ ends that are trimmed by a nuclease before extension by Pol θ. In some polymerases, the same active site can be used to catalyze both polymerase activity and endonucleolytic cleavage. For example, some RNA polymerases reorganize their active site to edit transcripts by cleaving off 1 or 2 nucleotides from the 3′ end.